1. Field of the Invention
The present invention relates to a lead frame for a multi-chip package (hereinafter, referred to as an MCP) in which two semiconductor chips with semiconductor integrated circuits including semiconductor devices are mounted in parallel in a single package, and to a semiconductor device using the lead frame.
2. Description of the Related Art
As semiconductor integrated circuits with high performance have been integrated with a high density, an MCP capable of mounting a plurality of semiconductor chips has been substituted for a package capable of mounting a single semiconductor chip. The MCP can implement high-density mounting and combine performances of semiconductor chips in different types of diffusion processes, so that the MCP has advantages of development period shortening and low production cost.
Now, a conventional lead frame will be described with reference to FIGS. 8 and 9.
FIG. 8 is a plan view showing a conventional lead frame. FIGS. 9A and 9B are cross sectional views showing the conventional lead frame. In FIGS. 9A and 9B, the cross sections of the semiconductor device using the lead frame of FIG. 8 are taken along line A–B in order to represent vertical variations of die pads thereof.
In the figures, reference numerals Za and Zb denote vertical variations of a die pad 2 in a Z-direction, that is, a direction perpendicular to a mounting plane thereof.
In the figures, reference numerals Za′ and Zb′ denote vertical variations of the die pad 2 in the Z-direction caused from counteraction thereof.
As shown in FIG. 8, the conventional lead frame includes die pads 1 and 2 which have different sizes and are mounted thereon with two semiconductor chips, a frame 3 surrounding the die pads 1 and 2 on four sides in a quadrilateral shape, suspension leads 4a, 4b, 5a, and 5b respectively extending from four inner corners of the frame 3 and supporting the die pads, a die pad connecting portion 6 connecting the die pads, a plurality of inner leads 7 arranged radially to surround the die pads, a plurality of outer leads 8 connected to the plurality of inner leads 7 and having distal end portions thereof connected to the inner side of the frame 3, and a tie bar 9 connecting the outer leads in an arrangement of a series of strips and surrounding quadrilaterally, within the frame 3, the die pads 1 and 2, the die pad connecting portion 6, and the inner leads 7, wherein at least one die pad and the die pad connecting portion are located to deviate from the center line L0 of the main plane of a resin molding area 10.
The die pad is located to deviate from the main plane center line L0 of the resin molding area 10 in order to secure a region where a plurality of bond pads formed on semiconductor chips and the inner leads are connected by means of metal wires and to reduce the lengths of the wires as much as possible.
However, in a lead frame for an MCP such as a conventional quad flat package (hereinafter, referred to as a QFP), the suspension leads are different from each other in shape and length, so that it is difficult to support the die pads in a balanced manner. In addition, although the die pad deviating from the main plane center line of the resin molding area is located to be aligned with the main plane center line of the die pad connecting portion, it is difficult to support the die pads in a balanced manner.
As shown in FIGS. 9A and 9B, in an unbalanced arrangement of die pads such as that of the conventional lead frame for QFP-MCP, supporting forces exerted on the die pads are caused to unbalance, and Z-directional vertical variations Za and Zb (and counteraction variations Za′ and Zb′) increase in assembling processes.
Due to the Z-directional vertical variation accumulated in the previous processes, there arises such a problem that resin molding defects occur in the molding process, the defects including package bending, voids, failure of resin filling, wire disconnection, exposure of semiconductor chips, and exposure of die pads.
In addition, in the trend of semiconductor devices, before and until the first half of 1990, thin small-sized products were developed by using a QFP resin thickness in a range of from 2.0 mm to 3.0 mm as a main stream of semiconductor devices. Since the second half of 1990, commercially provided products have had a resin thickness in a range of from 1.0 mm (in TQFP, an attached height is 1.2 mm or less) to 1.4 mm (in LQFP; an attached height is 1.7 mm or less). Such products have become the mainstream in the recent trend. In addition, from the beginning of 2000, products having a resin thickness in a range of from 0.7 mm to 0.8 mm (in WQFP; an attached height is 1.0 mm or less) have been developed and commercially provided. As the QFP resin thickness becomes smaller and smaller, there arises a dominant problem that the resin molding defects are caused by the Z-directional vertical variations of die pads.